Project Summary: Patients with salivary gland (SG) dysfunction suffer from dry mouth, dysphagia, increased oral infections, mucositis and generalized oral discomfort, which severely affect their quality of life. Regeneration of secretory units and restoration of gland function by activation of resident stem cells may offer an effective treatment option for these patients. However, we lack a clear operational understanding of the cellular and molecular mechanisms that could be harnessed to induce renewal and regeneration in the gland. Mouse submandibular gland has been extensively used as a model to study renewal and regeneration in the SG. The glandular compartment in this model is composed of two secretory cell types including acinar and granular ductal cells that are separated by relatively undifferentiated intercalated duct cells. Whether stem cells contribute to the maintenance and regeneration of differentiated cell lineages is controversial. Using modern genetic tools to study cell renewal in the secretory complex, we recently provided the first clear evidence for a stem cell population in the intercalated duct contributing to development and homeostasis of the granular ducts. Our ongoing studies, using a well-established model of reversible injury, unveiled a remarkable plasticity and multi- lineage regenerative capacity of these stem cells to regenerate the entire secretory complex including acini and their contiguous intercalated ducts. What triggers this uni- to multi-potency switch in stem cells and how their proliferation and differentiation potential are regulated is currently unknown. We hypothesize that ductal stem cells fate and potency is controlled by cues from their microenvironment or niche. To test this hypothesis we will use our established mouse models, cell sorting strategies and transcriptome analysis t o decipher the unique molecular signature of stem cells in comparison to their differentiated progeny to inform on components of the niche and gain valuable insights into regulation of stem cell proliferation and differentiation potential during homeostasis (Aim 1). We then take a systematic approach in quest of signals that control the remarkable plasticity and potency of ductal stem cells in response to injury (Aim 2). This proposal will result in discovery of novel markers for adult SG progenitor cells and signaling pathways that may be regulating SG stem cell potency under normal and regenerative conditions. Successful completion of these studies will provide the foundation for translational studies for treatment of SG hypofunction and might also have relevance for suppressing uncontrolled growth and neoplasia.